1. Field of the Invention
The present invention relates to a semiconductor device which is operable at an extra-high frequency and an extra-high speed.
2. Description of the Prior Art
Up to the present, as a semiconductor device operable at an extra-high frequency and an extra-high speed, there have been a schottky gate field effect transistor (MESFET) using a compound semiconductor such as GaAs, and two dimensional electron gas FET using n-AlGaAs/GaAs hetero junction, as described for example in a Japanese book "Compound semiconductor device handbook" published from Science Forum Co., Ltd., Japan (1986). Such FETs however have poor capability of driving a large current and a relatively large source resistance, which limit their high frequency and IC. For example, in the MESFET, increase of carrier density in a channel is limited by lowering of gate breakdown voltage allowance and, in the two dimensional electron gas FET, the maximum electron density is smaller and further reduction of electron density and instabilities occur at a low temperature owing to n-type doping of AlGaAs which causes many traps of, what is called, DX centers.